1. Field of the Invention
The present invention relates generally to explosively formed penetrator warheads of the type used to attack an armor protected target and, more specifically, to an improved method and apparatus for assuring the explosive formation of a penetrator having aerodynamically stabilizing fins to form a more effective penetrator.
2. Prior Art
The explosively formed penetrator (EFP) warhead also known as explosively formed projectile, self forging fragment, Misznay-Schardin Charge, and the P-charge employs the method of explosively forming a metal liner into a single compact fragment and projecting it at armored targets at extremely high velocity. Upon impacting the target in excess of 2000 m/s an EFP deposits an enormous amount of kinetic energy at extremely high rates.
It is well known in the armor piercing projectile art to provide a deformable metallic insert (often called a warhead liner) for a hollow charge armor piercing projectile wherein the liner is collapsed by the detonation of the charge into an elongated dart-shaped projectile capable of penetrating the shell of an armored vehicle or the like. Inserts of this type have been disclosed for example in U.S. Pat. Nos. 3,217,647 and 3,732,816.
The earliest published demonstration of such a device was by R. W. Wood in 1936. During the early to mid-seventies, EFP technology escalated significantly, primarily because of two simultaneous developments: (1) the success of computer simulation techniques to model the EFP device, and (2) several system concepts sponsored by both the Army and Air Force that used EFP technology. This work demonstrated that virtually all practical axisymmetric shapes can be explosively formed by varying the contour and thickness profile of the metal liner in the proper way. In fact, many shapes, such as compact spheroids, long rods, hollow cups, and rods with a conical flare for aerodynamic stability have been demonstrated.
It is also well known in the art to provide such insert or liners with exotic shapes or material variations which are designed to produce wing stubs or rear end flares upon full deformation of the penetrator, for aerodynamically stabilizing the projectile in flight to increase its penetration performance.
The addition of forming fins as a means of providing aerodynamic stability to an EFP has several advantages over the conventional drag cone or flared tail. By replacing the drag cone with fins aerodynamic drag is reduced increasing terminal velocity at current state-of-the-art standoffs or increasing the current standoffs with no loss in terminal velocity. Also by forming fins additional liner material is concentrated towards the EFP's axis of symmetry, hence, increasing its penetration capability over that of an EFP with a hollow flare. In addition it is known that every EFP has some degree of nonsymmetry in the flare due to random buckling during formation. With fins the EFP is buckled in a controlled manner hence, decreasing random buckling and increasing formation repeatability. Finally by inducing spin into the EFP by canting the fins aimpoint accuracy is increased over that of the conventional flared EFP.
In U.S. Pat. No. 4,590,861 the disclosed insert is provided with a non-constant or varying material thickness extending in the centripetal direction in which the insert incorporates peripherally mutually offset centripetally extending zones with a material thickness which is constant in the centripetal direction and which alternate with centripetally extending zones having a non-constant varying material thickness. Similarly, in U.S. Pat. No. 4,714,019, the insert comprises a flat disk having differing material properties in the inner and outer regions which result in varying dynamic material behavior during explosion deformation. In the disclosed embodiment, the outer regions of the flat disk have a greater material hardness than the central regions of the disk.
Unfortunately, each such prior art liner while being advantageous from the standpoint of producing trajectory stabilizing rear end formations during the explosive forming process, presents significant disadvantages from the standpoint of production and cost. Such exotic variations in material shape or hardness or other such parameters require special time consuming and costly production processes as compared to a substantially uniform thickness and simply shaped liner. There has therefore been a long felt need for an explosively formed penetrator liner apparatus and method of production which provides the aforementioned advantages of rear end aerodynamically stabilizing fins or the like, but without the production and cost disadvantages of the prior art.